In general, EVOH copolymers have various excellent properties such as oxygen impermeability, mechanical strength, etc., and find application, as they are, in many uses as films, sheets, materials for containers, textile fibers, etc. However, this copolymer gives rise to a variation in the thickness of the product in the molding process for manufacturing a film or a sheet, with a consequent reduction in the marketability of the product, and, because of the shortcoming in stretchability and flexibility, gives rise to non-uniform drawing during deep drawing and other processes involving a stretching force, or pinholes during the use of the product, thus imposing serious limitations on its application as a raw material for packaging. The oxygen barrier of EVOH copolymers is also greatly reduced when the relative humidity (RH) increases.
In order to overcome these drawbacks, it has been attempted to laminate a material made of an impermeable resin, such as a polyolefin film, on a sheet of EVOH copolymer or to improve the stretchability and flexibility of the molding by incorporating a polyolefin into the EVOH copolymer.
Application JP 05098084, published on Apr. 20, 1993, describes blends of 5 to 80 parts of polyethylene, 10 to 90 parts of EVOH and 10 to 90 parts of polyethylene grafted by an unsaturated carboxylic acid necessary for making the polyethylene and EVOH compatible.
It has been found that these compositions exhibit an oxygen barrier only if EVOH is the major component in the blend and that this also depends on the compatibilizer. However, compatibilization between EVOH and polyethylene using the grafted polyethylene described is not very good, the blend is not reproducible and it is difficult to make it into film.
U.S. Pat. No. 5,322,877 describes compositions similar to the previous ones but comprising, in addition, a salt of an alkali metal and a fatty acid. The amount of EVOH is from 30 to 70% of the whole consisting of the EVOH, the polyethylene and the granted polyethylene.